Antarctic Melt Releasing DDT, Tainting Penguins
for National Geographic News
|May 12, 2008|
Poisonous chemicals that had been locked in ice for decades are now being released as climate change melts Antarctic glaciers, researchers report.
The chemicals, including the pesticide DDT, are seeping into the polar ecosystem and finding their way into wildlife populations.
Scientists made the discovery when studying the levels of pollutants in the fat and eggs of Adélie penguins.
DDT has been banned or severely restricted since the 1970s because it and other so-called volatile organic compounds were shown to cause reproductive ailments in animals.
In birds, for example, DDT breaks down into DDE, which can block calcium absorption and cause the birds to lay eggs with thinner shells.
With the chemical no longer in widespread use, scientists expected to find lower levels in Adélies.
"We were surprised to find that levels had not declined but had stabilized," said Heidi Geisz, a researcher at the Virginia Institute of Marine Science.
What's more, a small amount of the chemical had not yet been broken down by the animals' metabolism, which suggested that a fresh source of DDT was somehow finding its way into the penguins' guts.
Locked in Ice
To solve the mystery, Geisz and colleagues began to search for the pathways that contaminants might have traveled.
Like their emperor penguin cousins, Adélies don't migrate out of Antarctica, so Geisz knew the birds must be encountering pollutants locally. (See an interactive map of Antarctica.)
She first measured the environment for DDT from Africa, where the pesticide is still used in some countries to control malaria-infected mosquitoes.
(Related: "DDT to Return as Weapon Against Malaria, Experts Say" [August 1, 2006].)
DDT easily evaporates into the atmosphere, and wind currents float it to the poles. There the air condenses and drops its contents as precipitation into the supposedly pristine Arctic and Antarctic environments.
But when Geisz checked air, surface water, and snow samples for DDT, they all came back negative, reinforcing the idea that the chemical was not coming from current spraying.
"We had to say, Wait a minute, we're not seeing it in the snow or actual ice, or in the water or air, so where's it coming from?" Geisz said.
"And of course the only place left with measurable levels of DDT was in the glacier meltwater."
Her team found that during its widespread use in the 1970s DDT had wafted to the poles and became trapped in glacial ice.
Now, as warming in the region causes glaciers to melt at a record pace, the decades-old chemicals are being released into the ecosystem.
Geisz and her team estimate that the amount of DDT melting out of glaciers is 2 to 8 pounds (1 to 4 kilograms) a year—not enough to cause any ill effects in seabirds.
However, it is still unclear whether the melting has already hit the peak deposits of DDT or if those are still to come.
Birgit Braune is research scientist at the governmental agency Environment Canada who studies contaminants in Arctic seabirds.
"Basically [Geisz's team] compared new data that they've collected with older published data, and while there have been changes in methodology, they've gone to great pains to acknowledge and address all the confounding factors," Braune said.
"Their argument certainly makes sense, and it's an intriguing paper to be sure."
Geisz said she now plans to study a whole suite of organic chemicals in Adélie penguins and compare her findings to other Antarctic seabirds that migrate in the winter.
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